Harvest schedule for first cutting alfalfa

Phil Kaatz<kaatz@msu.edu>, Michigan State University Extension - May 19, 2015

Growing degree day differences abound across Michigan in 2015 from north to south.

Alfalfa producers wanting to harvest alfalfa according to forage quality will want to keep a close eye on the growing degree days (GDD) in the next 10-15 days. Using the calendar as the standard for harvesting alfalfa can lead to forages harvested at neutral detergent fiber (NDF) levels unsatisfactory for production goals. The importance of harvesting a hay crop on time can make a big difference in the fiber and energy levels for alfalfa. There is a usually a short window of opportunity to harvest alfalfa at a particular goal since NDF levels can change rapidly with increasing temperatures. Many dairy producers have a goal of 40 percent NDF. Data collected over a period of years suggests that an growers using an upright silo should begin harvesting at 750 GDD for alfalfa with 40 percent NDF + 3 percent most years. The current recommendation for producers using bunk silos is to begin cutting at 680 GDD corresponding to value of about 38 percent NDF. Using GDD is an important tool that should only be used for first cutting.

Alfalfa GDD is calculated by averaging the daily high and low temperatures for a 24-hour day, dividing by 2 and then subtracting the base of 41degrees Fahrenheit. The season total is the sum of daily growing degrees beginning March 1 through today. Anything less than 41F gets zero GDD for the day. Example: the daily high and low for today was 60F and 40F. The average is 50 F, minus 41F (base) equaling 9 GDD. Current information is available at weather stations placed throughout Michigan. To get information for a weather station near you, go to Michigan State University Enviro-weather.

2015 Growing degree days base 41 F (average method) beginning March 1 from MSU Enviro-weather.
Location (number of reporting stations)		Current GDD base 41 F	Predictions GDD base 41 F
	Date	May 18	May 24
Southwest (15)	Ave.	609	716*
	High	667	765*
	Low	494	611
South Central (10)	Ave.	590	707*
	High	667	786*
	Low	529	645
Southeast (4)	Ave.	562	684*
	High	595	729*
	Low	519	636
West Central (12)	Ave.	511	614
	High	598	716*
	Low	443	515
East Central (16)	Ave.	485	587
	High	582	697*
	Low	407	495
North Central (4)	Ave.	371	431
	High	395	457
	Low	342	397
Northeast (1)	Ave.	330	403
Northwest (9)	Ave.	373	441
	High	432	495
	Low	310	375
Upper Peninsula (3)	Ave.	279	328
	High	328	396
	Low	231	276

* Represents target number above 680 GDD for bunk silo harvest starting point. Target number is 750 GDD for upright silo starting point.

Growers with alfalfa and grass mixed stands should not use the GDD method to establish your cutting schedule. Consider harvesting these fields before harvesting the pure alfalfa stands. Grasses have higher NDF content than alfalfa cut at the same age. Spring harvest of alfalfa-grass mixtures is based on alfalfa maximum height and the proportion of grass in the stand. Michigan State University Extension suggests that producers consider harvesting fields that have the most grass first so purer alfalfa stands can be harvested at the appropriate NDF levels. If wet weather delays harvest, you may want to harvest the purest alfalfa stands first since fields with grass will likely be past the optimum NDF levels and may be better used for dairy rations requiring higher fiber, or for dry cows and heifers.

Another method for evaluating the current stage of maturity for alfalfa is the PEAQ (Predictive Equations for Alfalfa Quality) stick method. This method takes more time because you need to walk your alfalfa fields and select several spots in the field to get an accurate reading. The PEAQ stick uses both alfalfa stem height and maturity to predict forage quality. One must be able to know the different stages of growth of alfalfa (early bud, mid bud, late bud, early bloom and full bloom). A study conducted in six states across a wide range of environments estimated NDF within three units of actual wet chemistry in 77 percent of samples collected. PEAQ sticks should only be used for first and second cuttings of pure alfalfa fields that receive adequate moisture and growing conditions.

For more information, contact Phil Kaatz at kaatz@msu.edu or 810-667-0341.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).